Question

Let four-digit numbers be formed by using the digits $2,4,6,8$ (when repetition of digits is not allowed). Then sum of unit digits of all the numbers is

• A. $120$
• B. $280$
• C. None of these
• D. $320$

Answer 1

The correct option is A $120$

If we fix the unit's place with $2,$ then $3!$ numbers can be formed with given digits.
Hence, total numbers ending with $2$ is $3!$.
Similarly, all other digits $4,6$ and $8$ also appear $3!$ times.
Therefore, sum of the digits in the unit's place is $6(2+4+6+8)=120$